1. Field of the Invention
The present application relates to a process for providing photovoltaic thin film semiconductor devices, in particular solar cells and other devices obtainable by such a process. This film semiconducting devices have a wide variety of applications. For example, solar cells incorporating amorphous silicon, microcrystalline silicon or polycrystalline silicon are employed to generate electricity from incident irradiation.
2. Background of the Prior Art
U.S. Pat. No. 4,721,535 discloses a solar cell wherein the p-type layer consists of three layers, which all comprise carbon and of which the middle layer is doped with Boron. As the composition is varied step wise, such layers can not be produced in a continuous process.
In the article "Fabrication of single pin type solar cells with high conversion efficiency of 13.0%" by K. Miyachi et al., a p-type layer is disclosed, which consists of two graded layers. In the first layer, the Carbon concentration is increased by increasing the proportion of dimethyl relative to silane. In the second layer this proportion in decreased. In this publication no doping of the layers is disclosed.
In the European patent application EP-A-0 437 767 a a-SiGe:H is disclosed, wherein a high band gap in the n-type layer is achieved by adding Carbon or Nitrogen. This will cause problems regarding alignment of the bands and a barrier between which the layer will be generated.